Prevention of Material Deterioration in ECM of Sintered Carbide with Iron Ions (2 nd Report)

This study focuses on electrochemical machining as a method of processing sintered carbide at high speed. Previous studies have suggested the possibility of using electrochemical machining to achieve the high-speed machining of sintered carbide. However, there has been strong resistance from industry against bringing sintered carbide into contact with a conductive liquid. This is because the material quality of sintered carbide is degraded by the elution of Co when in contact with a conductive liquid. In previous reports, the authors have shown that it is possible to control the two modes of Co elution occurring during electrochemical machining: the elution from sintered carbide in contact with an electrolyte and the selective elution of Co arising from differences in the speeds of the dissolution of tungsten carbide and the elution of Co when sintered carbide is connected to an electrical source for processing. It is possible to control the elution of Co from sintered carbide in contact with an electrolyte by adding Co ions to the electrolyte, which increases the Co ion concentration. In addition, the excessive elution of Co can be prevented by using a bipolar electrical source for machining. Although we have shown that it is possible to carry out the electrochemical machining of sintered carbide without degrading its quality, the addition of large amounts of Co ions to the electrolyte is expensive. Therefore, we attempted to prevent the degradation in the quality of sintered carbide by adding iron ions instead of Co ions, and we confirmed that the addition of Fe ions has the desired effect. However, the Fe 2+ ions in the solution are easily oxidized to Fe 3+ ions with time, and the Fe 3+ ions yield no protective effect for sintered carbide. In our previous report, we discussed a method to bring the electrolyte into contact with Fe to prevent the oxidation of Fe 2+ ions to Fe 3+ ions and proposed the use of an iron filter. In the present report, we verify the effect of the iron filter.